Physiological conditions of a subject can provide useful information about the subject's health status, such as to a physician or other caregiver. Devices may be implanted within a patient's body for monitoring certain physiological conditions. For example, a vascularly implantable pressure sensor can be used to measure blood pressure, however, the resulting measurement provides only an absolute pressure value of the immediate anatomical environment, which does not take into account ambient barometric pressure external to the body. Such a vascularly implantable pressure sensor is typically not capable of communicating gauge pressure because it is isolated from the ambient pressure external to the body.